AND ON THIS DAY THE SHARK WAS BROUGHT BACK TO LIFE!
10-02-2015, 11:25 AM
#1
Instructor
Thread Starter
AND ON THIS DAY THE SHARK WAS BROUGHT BACK TO LIFE!
some of you know my struggle.. i bought my first shark a few months ago as a summer project.. the car was sitting for years but it ran.. well sort of ran... had some major issues to work out.. i had no clue what i was getting myself into. this is my first porsche.. yikes.. i consider myself a decent mechanic but the engineering behind these early L jet FI cars is just WOW.. no words to explain.. i spent countless nights on rennlist reading posts and watching youtube videos.. my car was running super rich!!.. i went down the rabbit hole myself instead of taking the car to a specialist... i was in for quite a journey. after doing all the routine stuff you normally do to a car thats been sitting for years (vacuum hoses/fuel pump/ filter/ plugs/wires/checked fuel pressure/spark... i couldnt figure this car out.. many of you helped me along the way and i appreciate all the help.. i ended up having the injectors cleaned/ AFM tested/ swapped L Jet brain etc etc etc.. nothing would help... i did everything i could to this car.. you name it i tried it .. nothing would solve my running rich issue..im talking sooo rich the car wouldnt even stay at idle when warmed up.. tons of raw fuel and black smoke out the tailpipes... i had finally thrown in the towel and made an appointment for a specialist to look at the car... today is the day they were suppose to come pick up the car.. i had it cleaned and ready..... the last thing i wanted to test this morning was to make sure the AFM was sending the proper reading to the L Jet brain.. i have checked these before but who knows maybe i missed something... anyways i realized that the temp I signal was NOT getting to the L Jet main harness plug pin... hmmmmm thats odd.. so i go back to the AFM plug and notice old electrical tape on the harness.. hmmm.. soo i undo the tape and notice that someone in the past had spliced in a resistor in the pin 27 wire(tempI) AND the resistor had broken off its connection to the wire.. OHH BOY I GOT SOO EXCITED!!! i removed the resistor and connect the to wires and start the car and KAPOW!! it RUNS!!! i couldnt believe it... i let it warm up in the driveway and the black smoke cleared up... took it for a drive around the block.. idles fine now, runs amazing . its my lucky day for sure!
thanks to all for helping me along the way.. now this shark has a date with the detail shop...woohoo!!
my only question is this.. Why would someone want to put a resistor spliced into that wire? to hold back signal from the temp sensor to the LJet brain? but why?
thanks to all for helping me along the way.. now this shark has a date with the detail shop...woohoo!!
my only question is this.. Why would someone want to put a resistor spliced into that wire? to hold back signal from the temp sensor to the LJet brain? but why?
10-02-2015, 12:37 PM
#3
Archive Gatekeeper
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What sort of 'filter' is applied to your pictures? Either you're using claymation or I ate the wrong brownies this morning. 
10-02-2015, 03:07 PM
#5
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Looks like massive amount of noise reduction in the photos to me...
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10-04-2015, 08:48 AM
#9
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These stories are priceless - the thrill of victory to overcome the other thing. Thank you.
If you find a reason to re-install a resistor on this wire, use a higher wattage resistor - it will be more robust to corrosion, vibration and people who handle cables as if they were rope. I think I would add something to stiffen the assembly, maybe two layers of shrink wrap.
If you find a reason to re-install a resistor on this wire, use a higher wattage resistor - it will be more robust to corrosion, vibration and people who handle cables as if they were rope. I think I would add something to stiffen the assembly, maybe two layers of shrink wrap.
10-04-2015, 10:21 AM
#10
They probably placed a resistor inline with the temp gauge to make the temp gauge reading more accurate. I had a Ferrari mech tell me that he had done this trick with an old 308 to fix a flaky temp gauge.
However unless you know the exact resistance to make the gauge accurate, you are just making a guess.
I wired a potentiometer (variable resistor) is line with the temp sensor to be able to calibrate the temp gauge with the FFDynamics electric fan I installed. The POT has a range of 0-25 ohms. One just has to turn the POT to adjust the temp gauge to reflect center with normal coolant temps.
Now when the coolant temp is 185-190F the temp gauge is exactly in the middle instead of being high. It took 16 ohms to center my gauge as measured with a MM, but your results may vary.
I know this fix is just putting lipstick on a pig and the gauge is still fundamentally inaccurate but at least I know the gauge is now reflecting the actual coolant temps as measured with an IR gun.
About your only alternative is to ignore an inaccurate gauge or wire an aftermarket temp gauge somewhere in the console.
Like the fix or not, but it does work.
However unless you know the exact resistance to make the gauge accurate, you are just making a guess.
I wired a potentiometer (variable resistor) is line with the temp sensor to be able to calibrate the temp gauge with the FFDynamics electric fan I installed. The POT has a range of 0-25 ohms. One just has to turn the POT to adjust the temp gauge to reflect center with normal coolant temps.
Now when the coolant temp is 185-190F the temp gauge is exactly in the middle instead of being high. It took 16 ohms to center my gauge as measured with a MM, but your results may vary.
I know this fix is just putting lipstick on a pig and the gauge is still fundamentally inaccurate but at least I know the gauge is now reflecting the actual coolant temps as measured with an IR gun.
About your only alternative is to ignore an inaccurate gauge or wire an aftermarket temp gauge somewhere in the console.
Like the fix or not, but it does work.
10-08-2015, 03:35 AM
#13
Instructor
Thread Starter
thank you guys.. i was speaking with a fellow mechanic friend of mine who has been helping me with the 928.. i told him the story today about the resistor and he mentioned it was probably placed there in the past because the car wouldnt pass emissions testing. so the resistor would make the signal to the LJet lower which would make the car run leaner and thus helping it pass emissions... keep in mind that someone also installed a new catalytic converter and new O2 sensor back probably when they installed the resistor.. in order to help the car get through the emissions testing... and somehow the resistor broke after that and they must have had forgotten what they did.. or something like that... haha just glad to get the damn thing to run correctly again.. im in the process of detailing it out and look forward to posting pix soon... thanks for reading
10-09-2015, 04:48 AM
#14
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Unlike the LH digital fuel injection system, the analog L-Jetronic module must have valid engine temperature and airflow meter voltages to work. Therefore when diagnosing no-start conditions with these 1980 to 1984 928s, it mandatory to verify these connections, because an open circuit will cause what Bruno has been suffering.
The LH fuel injection systems will work with no temperature or MAF connection to the module, just not work very well.
Rich
1993 928 GTS Cover Girl
1987 S4 Rennsport Reunion IV and V Shuttle
1979 5-speed rescue
1979 5-liter track beast
The LH fuel injection systems will work with no temperature or MAF connection to the module, just not work very well.
Rich
1993 928 GTS Cover Girl
1987 S4 Rennsport Reunion IV and V Shuttle
1979 5-speed rescue
1979 5-liter track beast